This is an interesting point. In the past, the Court has essentially said that you could do things like this. For example, it’s obviously not a violation of the 4th Amendment to have stakeouts and follow suspects. But in the past it has always been very expensive for law enforcement and intelligence agencies to do things like this, and they would never expend resources to surveil people unless they had a pretty good sense they were doing something wrong. But in today’s world, it’s pretty easy to use electronic surveillance, GPS tracking, etc., and we can no longer rely on limited resources/cost as preventing excessive surveillance.
The Court seems to have shown a growing recognition this in the recent GPS tracking case, US v. Jones, where 4 justices expressed concern over the the implications of new technologies.
This is still supposed to happen. The repository of collected metadata is still only supposed to be searched when they have articulable suspicion. The difference is that the archive allows for mining of past data/communications once that suspicion exists, and not only future data/communications.
